Genes that are down-regulated in low KPY samples in our study have also been found to be preferentially expressed in xylem tissues in several other studies. This includes microarraybased studies in tree species which compared different tissue types such as xylem vs phloem, shoot apical meristem vs mature xylem and leaves vs xylem. All of the genes that are up-regulated in low KPY samples belong to categories such as Sertraline hydrochloride biotic and abiotic stress response, defense response and apoptosis. Since low KPY trees were generally smaller, this suggests that these trees experienced environmental stress, most likely due to competition Vitamin C effects in the trials. A transcriptome study in Arabidopsis thaliana revealed intra-specific competition resulted in activation of genes related to biotic and abiotic stresses. Slow growing trees have been observed to have lower KPY in other tree species including E. globulus and Populus tremuloides. In a study involving E. globulus and E. nitens trees, Downes et al. showed that irrigated trees had higher KPY compared to trees grown in rain-fed conditions. This suggests that trees with lower growth due to environmental factors, particularly water availability, are directing proportionally less carbon into cellulose. Thirty percent of SNPs with DAE occurred in 313 genes that had DGE between high and low KPY trees. It is likely that some of these SNPs may be cis-acting regulatory variants controlling the expression of the gene in which they occur. Because there are more than one SNP from a gene in many instances, some of the SNPs in some genes will be in high linkage disequilibrium with the true cis-acting SNP. The remaining 1463 SNPs showed DAE but no DGE. Some of these variants may be trans-acting variants or coding variants in transcription factors that affect their binding affinities to target genes. Cis-acting variants that are present within genes influence traits through their effects on gene expression while trans-acting variants affect transcript levels in target genes by interacting with cis-regulatory sequences.